Reed switch for rapid cycle,high power applications

ABSTRACT

Each of the reeds is preloaded against a thicker post that extends along it at its side opposite the other reed. Each has an anchor portion flatwise secured to the post, a flat armature portion, and a thinner neck portion connecting the anchor and armature portions and extending obliquely to them. The reeds are bimetallic, of &#39;&#39;&#39;&#39;Kovar&#39;&#39;&#39;&#39; and &#39;&#39;&#39;&#39;Niromet 42,&#39;&#39;&#39;&#39; with the latter next to the post. A molybdenum contactor carried by one reed cooperates with a tungsten contact on the other. Operating parts are hermetically sealed in an envelope evacuated to a deep vacuum.

United States Patent I 1 I 1 I 1 I 1 Inventor John D. Santl West Allis,Wis.

Appl. No. 818,913

Filed Apr. 24, I969 Patented June 22, 197i Assignee Briggs & StrattonCorporation Wauwatosa, Wis.

Continuation of application Ser. No. 714,490, Mar. 20, 1968, nowabandoned.

REED SWITCH FOR RAPID CYCLE, HIGH POWER APPLICATIONS 25 Claims, 7Drawing Figs.

Int. Cl. H0111 1/04 FleIdotSearch ZOO/166C,

166.l, 166 B; 335/154, 196; 337/] I I, 379

[56] References Cited UNITED STATES PATENTS 2,400,003 5/1946 Hensel etal. 200/166 (C) 3,3 I 7,869 5/1967 Funke 335/154 3,327,262 6/ I 967Bongard et al.... 335/154 3,229,063 1/1966 Sakatos 335/154 PrimaryExaminer-H. 0. Jones Attorney-Ira Milton Jones PATENIED JUH22 l97l 3;586; 809

sum 2 or 3 "NIROMET 42" "KOVAR" FIG-.7.

FULL GAP ZERO GAP (REEDS ENGAGED) 'NVELNTOR Juhn 17. 55min. BY

ATTORNEY REED SWITCH FOR RAPID CYCLE, HIGH POWER APPLICATIONS Thisapplication is a continuation of my copending application Ser. No.714,490, filed Mar. 20, 1968, now abandoned.

This invention relates to magnetically actuated reed switches and moreparticularly to a reed switch that is especially well suited for use ina circuit that carries substantially high power and must be opened andclosed at recurrent intervals of short but variable duration.

Magnetically actuated reed switches have been available for many years,and have long been recognized as potentially use- 1 ful in manyapplications. In practice, however, such switches have heretofore hadlimited utility because of their inability to operate satisfactorily inhigh volt-ampere circuits and to respond accurately to short, rapidlyrecurring cycles of buildup and decay of a magnetic actuating field. Forexample, one such switch, recently placed on the market and consideredto represent an advanced state of the art, was rated for 240 operationsper minute and to break 3 amps. at 125 volts, AC, and 2 amps. at 250volts, AC.

To some extent this recent switch sacrificed high cycle speed to gainpower handling capability, since previously marketed reed switchesintended for lower power were capable of cycle speeds on the order of 60operations per second.

Operating frequencies many times the 240 pm of this recent switch areneeded for numerous applications in which reed switches are potentiallyuseful (e.g., computers); and power ratings substantially higher than500 volt-amperes at break are likewise essential in many cases (e.g.,machine tool controls), and are desirable in all cases where they can beobtained without sacrificing other important characteristics.

For broadest utility, a reed switch should have a long service life aswell as a high cycle speed and a high power rating. The above mentionedrecently marketed reed switch had an advertised life expectancy of only500,000 operations when breaking 3 amps. at 120 volts AC. Underconditions of rapid cycling this would represent an extremely shortservice life, e.g. less than 40 hours at 240 0pm.

The reed switch disclosed and claimed in US. Pat. No. 3,315,193, issuedApr. 18, 1967 to J. D. Santi, has been found to provide consistentlyaccurate timing of make and break at frequencies of more than 200operations per second, as well as at all lower cycle speeds. But whilethe invention of that patent achieved very high cycle speeds, it did notsolve the long standing problem of providing a reed switch with bothhigh cycle speed and the capacity for handling large amounts of power.

The present invention has as its general object to achieve a substantialadvance over the state of the reed switch art represented by US. Pat.No. 3,315,193, and, specifically, to provide a reed switch that not onlycompares favorably in cycle speed with the switch of said patent, but inaddition, has the ability to break circuits carrying on the order of1,500 volt-amperes, and has a service life expectancy on the order ofhundreds of millions of operations at its rated power.

In general, for a reed switch to afford reliable responses to changingmagnetic fields, the resilient flexing bias of its reed or reeds, bywhich its contacts are separated for switch opening, should be arelatively light one; and in addition, for it to close and open inaccurately timed relation to the buildup and decay of a rapidly cyclingmagnetic field, the normal gap between its contacts should be relativelysmall. A switch that meets these requirements tends to have relativelylight contact pressure in its closed condition, and therefore, to avoidhigh contact resistance, prior reed switches usually had contacts ofcopper or precious metal operating in an inert gas. But such contactstend to stick and erode when handling high power, and therefore thecapability for controlling substantially high power has been regarded asincompatible with the requirement of a reed switch, and particularly oneintended for rapid cycling.

Most of the causes of contact sticking'can be overcome with the use oftungsten contacts operating in a deep vacuum environment. Because of thehigh melting temperature of tungsten, tungsten contacts in deep vacuumcan interrupt higher currents than contacts of any other known materialwithout the occurrence of welding of the contacts or arcing betweenthem; and because of the hardness of tungsten, frictional sticking oftungsten contacts is also unlikely.

However, when contact separating force is limited, as in a reed switch,tungsten contacts in a deep vacuum, when breaking a high voltage, tendto reclose under the influence of electrostatic attraction. Tounderstand why such reclosure occurs, it must be borne in mind thatalmost every circuit is more or less inductive, and that tungstencontacts in a deep vacuum can separate without drawing an are throughwhich energy in the circuit can be dissipated. Therefore, as thetungsten contacts initially separate, a high voltage surge is induced inthe circuit and a large potential difference appears between thejust-separated tungsten contacts. Whether or not the electrostaticcharge between the contacts will reclose them depends upon themechanical energy available for separating them. If the contacts canreclose, the high current surge due to the distributed capacitance inthe circuit will usually be sufficient to melt the contacts and weldthem together.

With the foregoing observations in mind, it is one of the generalobjects of this invention to provide an electromagnetically actuatedswitch that is responsive to relatively small actuating forces but isnevertheless capable of breaking circuits that impress very highpotentials across its contacts, without switch failure due to contactsticking.

More specifically, it is an object of the present invention to provide ahigh cycle speed reed switch capable of controlling circuits thatimpress substantially high voltages across its contacts at circuitopening, and wherein means are provided for overcoming sticking of theswitch contacts due to any of the causes of contact sticking, includingreclosure due to electrostatic attraction between them.

A reed for a reed switch is a tuned element which vibrates at somenatural frequency and which thus tends to have different responses atdifferent rates of cyclical buildup and decay of a magnetic actuatingfield, depending upon whether or not the frequency of a buildingmagnetic field is in phase with the vibration of the reed following animmediately prior switch opening.

Nevertheless it is another object of this invention to provide a reedswitch that responds accurately to a cycling magnetic field of anyfrequency up to the maximum for which the switch is intended, saidmaximum being on the order of hundreds of cycles per second.

Another general object of this invention is to provide a very versatilereed switch that is adapted for very rapid cycling and is suitable forhigh voltage-high current applications, but which nevertheless has arelatively low resistance when closed so as to be well suited for lowvoltage applications where switch resistance must be kept to a minimum.

Another general and very important object of this invention is toprovide a reed switch that has a very long service life expectancy evenin high power DC applications.

The useful life of a switch depends upon the current that it is requiredto interrupt, particularly if it must always open when current isflowing in the same direction, as in a DC circuit.

It is well known that even when a switch opens without the occurrence ofa spark or are between its contacts, some transfer of material betweenits contacts nevertheless takes place at each opening. This arclesstransfer, which is known in the art as low voltage phenomenon," alwaystakes place from the positive contact to the negative one. It occurswith tungsten contacts operating in air or in a deep vacuum, as well aswith contacts of the other metals, operating in any environment. When aswitch is used in DC service, arcless transfer of material always takesplace in the same direction, and the transfers occurring in successiveopenings are cumulative so that the service life of the switch dependsupon the volume of its contact material and the current to beinterrupted. The same switch, operating in comparable AC service, willnormally have a substantially longer useful'life because the switch doesnot always open at the peak current in the cycle and, further, becauseeach contact is the positive one in about 50 percent of the openings ofthe switch so that material transferred during any one opening will betransferred back to its original site in a subsequent opening.

With the foregoing in mind, it is another object of this invention toprovide a switch that has contacts which overcome to a very substantialextent the problem posed by the low voltage phenomenon just described,so that the switch of this invention has an extraordinarily long usefullife even in high current DC applications.

More specifically, it is an object of this invention to provide a switchfor relatively high power applications, having contacts which permit anincipient arcing to take place at each opening of the switch, andwherein the incipient arcing thus permitted offsets to a substantialextent the transfer of material from the positive to the negativecontact that also occurs at each switch opening, to thus afford theswitch of this invention a long useful life, even in DC service.

Still another specific object of this invention is to provide a reedswitch having each of its reeds normally engaging a post or rebound stopunder bias, so as to have a yielding preload in accordance with theteachings of the above mentioned US. Pat. No. 3,3l5,l93, and wherein thereeds can have such a preload of a predetermined value in the finishedswitch even though they are heated to a substantially high temperatureduring the course of manufacture of the switch.

It is also a specific object of this invention to provide a reed switchof the character described that can be operated under widely varyingambient temperature conditions without any change in the value of thebiasing force which the reeds exert against their posts or reboundstops.

Another specific object of this invention is to provide a reed switchfor rapid cycling having refractory metal contacts that operate in adeep vacuum environment and having reeds that can be outgassed beforeassembly of the switch is completed without losing their preload, sothat the deep vacuum environment for the contacts will be maintainedduring a long service life of the switch.

With these observations and objects in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings. This disclosure is intendedmerely to exemplify the invention. The invention is not limited to theparticular structure disclosed, and changes can be made therein whichlie within the scope of the appended claims without departing from theinvention.

The drawings illustrate one complete example of the physical embodimentof the invention constructed according to the best mode so far devisedfor the practical application of the principles thereof, and in which:

FIG. 1 is a view in side elevation of a reed switch embodying theprinciples of this invention with a portion of its envelope shown brokenaway, the switch being illustrated in its normal open condition;

FIG. 2 is a view similar to FIG. I but showing the switch in its closedcondition;

FIG. 3 is a disassembled perspective view of the components of theswitch of this invention that are inside its envelope;

FIG. 4 is a view in front elevation of the reed assembly that includesthe contactor;

FIG. 5 is a side view on an enlarged scale of a reed element of theswitch of this invention;

FIG. 6 is a graph of the relationship between temperature and linearexpansion of each of three metals used in the reed of the switch of thisinvention; and

FIG. 7 is a graph of the forces acting upon a reed in the switch of thisinvention.

Referring now to the accompanying drawings the numeral 5 designatesgenerally a reed switch embodying the principles of this invention,comprising a pair of elongated, resiliently flexible, magneticallypermeable reeds 6 and 6' enclosed in an elongated hermetically sealedenvelope 7 of glass or the like. The envelope is evacuated to a deepvacuum. Extending through the sealed ends of the envelope are a pair ofelongated terminal members 8 and 8, one for each of the reeds 6 and 6'.Each of the terminal members supports its reed at its inner end and hasits outer end portion exposed to provide one of the terminals 9, 9' ofthe switch.

The reeds 6 and 6' extend axially inwardly from their respectiveterminal members 8 and 8, and their free tip portions are disposed inlengthwise overlapping relationship in the medial portion of theenvelope, normally spaced apart laterally by a predetermined distance todefine a gap 10. Under the influence of a magnetic field that threadsthe reeds and the gap 10, the reeds are flexed to bring theiroverlapping tip portions into contact with one another.

Also secured to the inner end of each terminal member 8,8 is anelongated, relatively stiff post or rebound stop which ex tendslengthwise along the reed at the side of the latter that is remote fromthe other reed, the post for the reed 6 being designated II and the postfor the reed 6 being designated 11. Since each reed is formed from flatstrip material, it can be said to have a rear surface that faces itspost and a front surface that faces the other reed.

Each reed normally engages its post under flexing bias so as to have arearward preload against the post in accordance with the teachings ofthe above mentioned US. Pat. No. 3,3 I 5,193, to which reference may bemade for an explanation of the advantages of this arrangement and themanner in which it affords extremely high cycle speed in a reed switch.

In accordance with the present invention the reed 6 carries a contactor12 which normally engages the rear surface of said reed 6 under forwardflexing bias and which has a contact portion 13 that projects forwardlyacross the tip of the reed 6 to be normally spaced from the reed 6 by adistance somewhat smaller than that across the gap 10 between the tipportions of the reeds themselves. As explained more fully hereinafter,the contactor has several functions, one of which is to prevent failureof the switch due to sticking of its contacts under high current surges.

Turning now to a more detailed consideration of the switch structure,the envelope 7 is preferably made of a length of glass tubing that hasits opposite end portions respectively drawn down around the terminalmembers 8 and 8' and fused to them to hold the terminal members 8 and 8'in rigidly fixed substantially coaxial relationship with one another andto provide hermetic seals around them.

As shown, the terminal members have their inner ends spaced apartaxially by a substantial distance, and each has a post I I, ll welded toits inner end; but it will be apparent that each terminal member couldcomprise an integral axially outward extension of its post. The lengthof each post is such that its tip is near the tip of its reed. Asexplained in US. Pat. No. 3,315,193, the post can be of either magneticor nonmagnetic material, but it should in any case be substantiallystiffer than the reed.

In accordance with the present invention, each of the reeds 6 and 6' hasa substantially flat anchor portion 15 adjacent its captive end, asubstantially flat armature portion 16 that comprises its free end, anda medial neck portion 17 that has a smaller cross-sectional area thanthe anchor and armature portions and is bent at obtuse angles to them.The neck portion is of course integral with the anchor and armatureportions and connects them. The anchor portion 15 of each reed flatwiseoverlies its adjacent post near the captive end thereof and can besecured to the post as by welding. The neck portion 17 extends obliquelyforwardly, away from the post and toward the reed tip. The armatureportion 16 is normally inclined toward the post to have its tip engagingthe post under rearward flexing bias.

It is intended that most of the flexing of the reed of this inventionshall take'place in its neck portion 17, and to this end the neckportion has reduced cross section area. Preferably the smaller crosssection area of the neck portion is obtained by reducing only itsthickness, as shown, to insure that the reed has a relatively flatspring rate, that is, to have the flexing stress forces in the reedincrease relatively gradually with forward displacement of the reed tiptoward the other reed. The significance of this will be evident fromFIG. 7, which represents the forces acting on a reed in the switch ofthis invention as the reed is magnetically actuated towards its switchclosing position. As a switch actuating magnetic field builds, itreaches a point at which the attraction between the tip portions of thereeds is sufficient to overcome their preloads and start them movingtowards one another. From that point the convergence of the reeds is somuch more rapid than the change in impressed flux that the impressedflux can be regarded as constant and the change in magnetic attractionforce (which is represented by the curve 26 in FIG. 7) can be regardedas due entirely to the convergence of the reeds. The change inattraction force between the reed tips is approximately inverselyproportional to the change in the flux leakage path area between them,and the curve 26 is therefore generally parabolic. The flexing stress ineach reed, represented by curve 24, increases linearly with forwarddisplacement of its tip. The difference between magnetic force andflexing stress at any instant is the force available to accelerate'thereed at that instant, and with a reed having a flat spring rate thisdifference grows rapidly as the reed moves toward the other, so that thereeds converge at an increasing acceleration.

Confining flexing of the reed mainly to its neck portion 17 furthercontributes to rapid response of the reed to a magnetic field in thatonly the armature portion 16 of the reed undergoes substantial movement.Since the mass of the armature portion is small as compared with that ofthe entire reed, the armature portion is readily accelerated by themagnetic and flexing forces that respectively act upon it in its switchclosing and switch opening motions. To achieve a correspondingly lowinertia in a reed of substantially uniform thickness along its length(like most prior switch reeds), the reed would have to be quite shortand would therefore be so stiff that its spring force curve would crossthe magnetic force curve and therefore the reed would not move to itsclosed position in response to a magnetic actuating fleld.

The neck portion 17 of each reed extends obliquely to its armatureportion l6 in order to minimize contact bounce when the reed tips engageone another. The tendency of the armature portion to rebound ismanifested in a vibration of the armature portion transversely to itsflat faces. But because the neck portion extends obliquely to thearmature portion, such vibration has a substantial component lengthwiseof the neck portion. Furthermore, the armature portion is relativelyshort. For these reasons, the frequency of reed vibration due to anycontact rebound tends to be high, and the amplitude of such vibrationtends to be small. Such high frequency vibration dissipates energyrapidly, and because of its low amplitude there is little energy todissipate. Therefore such make bounce as may occur in the reed switch ofthis invention poses no practical problem, even at the fast closurerates that are a concomitant of high cycle speed.

It will be understood, of course, that the provision of a post orrebound stop for each reed, against which the reed is preloaded, furthercontributes to the minimization of make bounce," permits the gap to be asmall one, and makes possible the use of reeds having a low spring ratein a switch intended for successive operations at short intervals.Without the posts 11 and 11 each opening of the switch would initiate ahigh amplitude, low frequency vibration of the relatively supple reedsthat would persist for a long time and would interfere with the timingof a directly subsequent reclosure of the switch. Instead, each reedrebounds from its post with a high frequency vibration of a very lowamplitude, as explained in U.S. Pat. No. 3,3 I5,I93.

Since the reeds engage one another with substantial force upon closureof the switch, the front surfaces of their tip portions have tungstencoatings '18. Because of their hardness, these tungsten coatings resistmechanical wear and they prevent the reed tips from stickingtogether asa result of cold welding or mechanical friction; and because of the lowcurrent flowing between the contacts 18 as they engage and separate, dueto the functioning of the contactor 12 as explained hereinafter, thosecontacts have no tendency to be welded together especially in view ofthe high melting temperature of tungsten. Because of the oxygen-freeenvironment of the tungsten contacts 18 in the switch of this invention,they do not oxidize and therefore their contact resistance remains lowduring the life of the switch, instead of increasing like the resistanceof contacts operating in air.

On the reed 6 there must also be a tungsten coating 23 that provides acontact engageable by the contact portion 13 of the auxiliary contactor12, for reasons explained hereinafter. This contact 23 can of coursecomprise a continuation of the tungsten coated area that forms thecontact 18 at the tip of that reed. (See FIGS. 3 and 4.)

As emphasized above, it is important that each of the reeds 6 and 6 beunder a rearward preload of a predetermined value by reason of which itnormally engages its post or rebound stop with a predetermined biasingforce. However, the reed assemblies comprising the reed 6 or 6, the postI l or 11 and the terminal member 8 or 8' are necessarily subjected tosubstantial heating at some time during manufacture of the switch. Acertain amount of heating of the reed assemblies is inevitable when theend portions of the envelope are melted and fused to the terminalmembers 8 and 8; and in fact heating of the reed assemblies is desirablein order to outgas them and insure that they will not emit gases thatwould destroy the deep vacuum in the envelope.

But if a monometallic reed were subjected to prolonged heating at orabove its stress relieving temperature, it would of course lose itspreload against its post.

A bimetallic reed, however, can be caused to have a desired preloadafter heating, and I have discovered two metals which possess propertiesthat complement one another in a remarkable manner and cooperate toafford an extremely desirable bimetallic reed. One of these metals, soldunder the trade names Therlo, Kovar and Rodar" (and hereinafter referredto as Kovar") consists of:

nickel 28.5 percent29.5 percent cobalt 16.5 percent-17.5 percentmanganese 0.5 percent Max.

iron balance The other, sometimes sold under the trade name Niromet 42"(and hereinafter so referred to) consists of:

nickel 40.5 percent-4| .5 percent carbon 0.02 percent max.

silicon 0.25 percent max.

iron balance Both of these alloys have a high magnetic permeance and lowretentivity so that they are well suited to be combined in a switchreed. They are also sufficiently resilient for the purpose. But thespecial suitability of this particular pair of alloys for the elementsof a bimetallic reed has to do with their thermal expansioncharacteristics. FIG. 6 is a graph of the linear expansion withincreasing temperature of these two alloys and of tungsten.

In the range from room temperature to about 600 F., the two alloys justdescribed have very nearly equal coefficients of linear thermalexpansion, so that a bimetallic reed that is made of them will notchange its preload even under the most extreme changes of ambienttemperature in which a reed switch could be expected to operate.Furthermore, within that temperature range the rate of expansion ofthese alloys is very nearly the same as that of tungsten, so that abimetallic reed of these alloys can be very satisfactorily provided withthe tungsten coating 18 on its tip portion without any danger that thetungsten coating will cause flexing of the armature portion of the reedunder temperature swings by which the preload of the reed would bechanged.

As may be seen from FIG. 6, the curves of expansion vs. temperature forthese two alloys are substantially linear in the temperature range justmentioned. At about 600 F., however, the curve of expansion of Niromet42" per degree rise in temperature turns upward and at values aboveabout 700 F. it again becomes linear, but at a steeper inclination thanbelow 600 F. The corresponding curve for Kovar continues upwardly in asubstantially straight line to about 750 and then gradually steepensuntil from about 850 upwardly it again becomes linear and is parallel tothe curve of Niromet 42 for temperatures about 700.

in accordance with this invention, a bimetallic reed is made by bondingtogether elements of Niromet 42 and Kovar and then rolling the bimetalbillet to the desired thickness to form a strip from which the reeds aremade. Each reed is secured to its post with the "Niromet 42" next to thepost and with the reed initially under a substantially higher preloadthan is desired for it in the finished switch. This reed assembly isthen heated to a temperature substantially in excess of 800 F., andpreferably on the order of 1,400" F. or above.

The maximum temperature to which the reed assembly is heated is notcritical, so long as the reed becomes hot enough to be incapable ofsupporting stresses. Nor is there any criticality in the time duringwhich the reed is maintained at the maximum temperature. Preferably,however, such heating is performed in a deep vacuum and the reedassembly is brought to a high enough temperature and held there for along enough time to outgas it.

As the temperature of the reed goes up through 600 to 800", the Niromet42 at the rear of the reed expands more rapidly than the "Kovar," andconsequently a portion of the initial preload of the reed against thepost is relieved. With further increase in temperature to the maximum,the reed is completely stress relieved, remaining in contact with thepost but without exerting any biasing force against it.

As the reed is cooled from its maximum temperature down to about 800",no stresses appear in it, since the two metals of which it is made arecontracting at the same rate. At 800 and below, the reed is capable ofsupporting substantially high stresses. As it cools through the range of800 to 600', the Niromet 42 contracts more rapidly than the Kovar andthe reed is bimetallically flexed into engagement with its post under abiasing force that can be accurately predetermined on the basis of therelative thicknesses of the two alloys comprising the bimetal. Since thetwo metals expand and contract at substantially equal rates attemperatures of 600 and below, this biasing force or preload remainsconstant at all temperatures from about 600 down to room temperature.

It is emphasized that the reed must be initially assembled to its postwith a substantially excessive preload, so that the tip of the reed willnot move forwardly out of contact with its post under the bimetallicflexing that occurs as the reed is heated through the 600-800 range. ifthe reed tip were permitted to move away from the post during heating,due to an insufficient initial preload, the final preload on the reedwould be indeterminate because it would depend in part upon the unknownspacing between the reed tip and the post at temperatures above about800. lf high enough, the value of the initial preload is not critical,since the final preload on the reed is purely a function of itsbimetallic flexing.

It will be understood that bimetal reeds according to this invention canbe made of other pairs of metals than "Kovar" and Niromet 42." In everycase, at least one of the metals comprising the reed must bemagnetically permeable; the rates of linear thermal expansion of the twometals must be substantially similar up to a certain value, which valueis within the range of temperatures at which both metals will supportstress; and the rates of thermal expansion of the two metals must bedifferent through a range of temperatures above that value, the metalhaving the higher rate of linear expansion in said range being at theside of the reed adjacent the post. For example, a fairly satisfactoryreed according to the invention has been made of Niromet 42 having atungsten coating along its entire length at its side remote from thepost,

the tungsten coating serving as the bimetal element having the lowerrate of linear thermal expansion in the high temperature range.

While the high cycle speed of the switch of this invention is in largemeasure due to the preload of its reeds 6 and 6' against the posts 11and 11, its ability to control high volt-ampere circuits is mainlyattributable to the contactor 12 that is carried by the reed 6, althoughas will appear in the course of the description, the contactor alsoperforms certain other important functions.

The contactor should be light in weight so that it does not greatlyincrease the mass of the reed 6 by which it is carried, and it must besubstantially resilient. These requirements are nicely met by molybdenumwire, which also possesses other very important advantages that arediscussed hereinafter.

The molybdenum wire contactor 12 is bent generally to an elongated Uthat has its legs 19 curved inwardly back upon themselves near theirfree end portions, around loops 20, to provide coplanar anchoringelements 21 that comprise the end portions of the length of wire. Theseanchoring elements flatwise overlie the front face of the armatureportion 16 of the reed 6 and they are welded or otherwise bondedthereto. By reason of joglike bends 22 in the legs 19 of the contactor,the anchoring elements 21 and loops 20 lie in a plane that is spacedforwardly from the plane of the remainder of the legs 19, and theportions of said legs that lie between the bends 22 and the bightportion 27 of the contactor define a spring arm which overlies the rearface of the armature portion 16 of the reed and which normally engagesthe armature portion under forward bias. At its bight portion 27 thelegs 19 of the contactor are spaced apart a distance substantially lessthan the width of the reed, but they diverge substantially toward theneck portion 17 of the reed and are spaced laterally from the side edgesthereof.

The bight portion of the contactor, which lies outwardly of the tip ofthe reed 6 and which comprises the contact 13 thereof, is bent at rightangles to its spring arm portion to pro ject forwardly across the tip ofsaid reed and beyond the front surface thereof so that with the switchin its normally open position the distance between the contact 13 andthe reed 6' is less than that between the reeds themselves.

As the reeds converge under the influence of a magnetic field, thecontact 13 on the contactor 12 engages the contact 23 on the reed 6'before the contacts 18 on the reeds themselves come into engagement.Because of the forward preload of the contactor against the reed 6, theforce required to bring the reeds into contact with one anotherincreases markedly when the contactor engages the reed 6'. In otherwords, once the contactor 12 engages the reed 6, the magnetic attractionforce acting on each reed is yieldingly resisted by the flexing force ofthe reed itself combined with that of the contactor 12. in H0. 7 theflexing force in the reed itself is represented by the curve 24, whilethe additional flexing force contributed by the contactor is depicted bythe curve 25. Note how the stepped curve for the combined flexing forcesof the reed and contactor nicely matches the curve 26 for the magneticforce acting to bring the reeds into engagement.

As pointed out hereinabove, when the reeds move toward one another underthe influence of a magnetic field, they are accelerated rapidly, rightfrom the beginning of their converging motion. Hence the reeds havesubstantial forward momentum at the instant the contactor engages thereed 6'. F urthermore, the magnetic force acting upon them at thatinstant is substantially large in relation to the flexing forces thatthey oppose to it. Since the contactor has forward preload, theseinertia and magnetic forces combine to very nearly eliminate contactbounce between the contactor and the reed 6'. Such slight vibration asmay occur immediately following impact of the contactor against the reed6 will be of very high frequency and small amplitude, due to the rapidlybuilding force with which the contactor is urged against that reed, andsuch vibration will therefore be very quickly dissipated.

After the contactor engages the reed 6, the armature portions of the tworeeds continue to converge rapidly, but the net spring force resistingtheir convergence does not increase quite as rapidly as the magneticforce attracting them into engagement, as will be apparent from FIG. 7.For this reason, as well as for the reasons pointed out hereinabove, thearmature portions of the reeds will have little tendency toward "makebounce" when they engage; but of course if they should rebound, theswitch will nevertheless remain effectively closed because the contactorwill remain engaged against the reed 6 with a contact forcesubstantially equal to the preload under which it normally engages thereed 6.

It will be noted that most of the flexing of the contactor takes placein its loop portions 20, which are located closely adjacent to the neckportion 17 of the reed. Hence the contact 13 of the contactor l2 and thearmature portion 16 of the reed 6 tend to swing about a common center,with the result that the contact 13, once engaged with its cooperatingcontact 23, has substantially no wear producing movement across thesurface thereof even though the armature portion of the reed 6 continuesto swing.

When the switch of this invention is fully closed, the contacts on thetwo reeds, comprising the tungsten coatings 18, provide a second currentpath through the switch, cooperating with the contacts 13 and 23 on thecontactor and the reed 6, respectively, to provide the switch of thisinvention with a relatively low net resistance whereby it is well suitedfor low voltage applications as well as for high power circuits.

While the contactor l2 performs very important functions in preventingmake bounce" and in maintaining low net resistance through the closedswitch, its role during switch opening is perhaps even more important.

As pointed out above, the reeds in the switch of this invention have avery flat and relatively low spring rate so that they respond promptlyand consistently to a rapidly building magnetic field. But sticking isalways a problem with switch contacts that must open a high powercircuit, even with high melting contacts operating in a deep vacuum;hence reeds of low stiffness could not, by themselves, exert sufficientcontact separating force to interrupt a circuit carrying high power. Inthe switch of the present invention, contact sticking from all causes isovercome by means of the contactor 12.

When a magnetic actuating field for the switch of this invention decays,separation of the reed tips somewhat increases the net resistance of theswitch, so that there is some potential difference between the contacts18. But the switch still remains effectively closed, owing to theengagement of the contactor with the reed 6'; and therefore theelectrostatic attraction between the contacts 18 is negligible and doesnot interfere with their rapid separation.

As the reed 6 moves rearwardly towards its post 11, it acquires a highvelocity, being accelerated by a combination of its own flexing forceand that due to the contactor preload. By the time it reengages the armof the contactor it has a large momentum. In consequence, the reed 6literally knocks the contactor out of engagement with the reed 6',overcoming any tendency for the contacts 13 and 23 to stick to oneanother. In thus providing for abrupt, forceful contact separation atswitch opening, the contactor enables the reed switch of this inventionto interrupt as high as 3,000 volts at 0.5 amp., with surge voltages atbreak that are as high as about 15,000 volts.

The current that a switch is required to break normally determines itsservice life expectancy. The switch of this invention has been found tohave a substantially longer useful life than prior reed switches evenwhen breaking currents of as high as amperes. At 0.5 amperes DC a switchof this invention has been found to be still useable after more than 200mil lion operations; and with lower currents its useful life wouldincrease in a nearly linear inverse relationship to current.

This long service life is due to the particular metals of which thecontacts 13 and 23 are made. As noted above, the contact 13 is anintegral part of the contactor 12, which is made of a single piece ofmolybdenum wire, and it cooperates with a tungsten contact 23 on thereed 6'.

If the contacts 13 and 23 were both of tungsten, operating in a deepvacuum, they would open without sparking or arcing, but a certain amountof tungsten would transfer from the positive contact to the negative oneat each switch opening. This transfer of material to the negativecontact is the well known low voltage phenomenon that occurs in arcless,sparkless separation of any switch contacts through which current isflowing. The reason for it is fairly well established. When a pair ofcontacts begins to make an arcless separation, their resistanceincreases rapidly as the contact force diminishes. Just as contactpressure goes to zero, the contacts are engaging each other at aninfinitesimal point through which all of the current in the circuit mustflow, and the energy thus charged into the contact metal in this verylocalized area heats it above its melting point, however high this maybe. The molten particle of metal thus formed is for a brief instant heldin place by surface tension, bridging the separating contacts, but asthe contacts continue to move apart its surface tension collapses and itsettles back onto the contacts. However, most of the molten metalsettles onto the negative contact, because the positive contact becomeshotter than the negative one. While the amount of metal thus transferredat each opening is relatively small, it varies in more or less directproportion to the amount of current carried by the switch.

When the switch of this invention is connected in a DC circuit, or inany circuit in which current is always expected to flow in the samedirection at the instant of switch opening, it should be so connectedthat its terminal 9 will be the positive one at the instant of switchopening and its terminal 9 will be the negative one. This is to say thatthe molybdenum contact 13 will be positive and the tungsten contact 23will be negative.

Hence when the contacts begin to separate, molybdenum from the contact13 will be transferred to the tungsten contact 23 in accordance with theusual phenomenon of low voltage material transfer. As the contactscontinue to move apart, the bridge of molten molybdenum across the twocontacts reaches its collapsing point, and a voltage difference appearsbetween the contacts. Under the influence of this voltage difference anabundance of electrons is emitted by the molten molybdenum on thenegative contact, producing a more intensified local heating there whichcauses ionized molybdenum to be emitted into the space between thecontacts.

Apparently a full plasma arc does not develop between the contacts, butthere appears to be an incipient arc in the nature of a cathode spot onthat part of the contact 23 to which molybdenum has been transferred.From that cathode spot most of the molybdenum ions are emitted, and suchions tend to move toward the anode, i.e., the contact 13 from which theyoriginated and from which they were transferred as molten molybdenum.Because of the deep vacuum environment of the contacts, they do notoxidize, and therefore the vaporized molybdenum which is redeposited onthe molybdenum contact 13 readily adheres thereto.

Thus the arcless transfer of molten molybdenum from the contact 13 tothe contact 23 that occurs in the initial phase of contact separation isin large measure offset or compensated for by the retransfer ofmolybdenum back to its original site, occuring by reason of theionization that takes place in the immediately succeeding phase ofcontact separation.

The tungsten does not take part in the transfer and retransfer describedabove, because its melting and vaporizing temperatures are substantiallyhigher than those of molybdenum and because in the very first phase ofcontact separation, when arcless transfer is occurring, the tungstencontact is the one to which such material transfer always takes place,so that molten molybdenum is being deposited onto it. At the powerlevels for which the switch of this invention is intended thetemperature of the cathode spot is determined by the characteristics ofmolybdenum; or in other words there is not enough power to supportionization of the tungsten once the molybdenum is vaporized off of it.

The foregoing explanation for the long service life of the switch ofthis invention in DC applications may not be complete, and may beinaccurate in some respects, but it is consistent with the results thathave been obtained with the switch of this invention and also with knownphenomena of switch contact behavior and the generally accepted theoriesfor them.

The explanation tends to be confirmed by what happens when the switch ofthis invention is wrongly connected in a DC circuit, with its terminal 9negative and its terminal 9' positive. Under those'conditions thenegative molybdenum contact 13 is sufficiently cooler than the positiveone so that an accumulation of tungsten develops on it, and the switchhas a substantially shorter useful life than when properly connected,failing when the tungsten contact becomes pitted or eroded to the pointwhere the substrate metal is exposed and the contacts stick because ofwelding or mechanical friction. Retransfer of the tungsten cannot occurunder these conditions because of the extremely high vaporizingtemperature of tungsten, which prevents the occurrence of an effectivecathode spot at power levels within the capabilities of the switch.

Further confirmation of the correctness of the above explanation appearsfrom the fact that the switch of this invention actually has a somewhatshorter life in a low voltage, low inductance circuit, even whencorrectly connected, than in the higher power circuits for which it isintended. Thus when a switch of this invention was installed in asubstantially noninductive circuit carrying 2 amperes at 1?? volts,molybdenum was found to transfer rather steadily from the positivecontact 13 to the negative tungsten contact 23, with no evidence ofretransfer. It should be pointed out that a circuit of this type (whichwould usually be in the nature of a heater circuit) is one in which areed switch would not be likely to have particular value, and that evenunder these comparatively adverse conditions the useful life of theswitch of the present invention was several times that of the best priorreed switches.

It will be seen from the foregoing explanation that the long useful lifeof the switch of this invention is due to the spread or differencebetween the melting and vaporizing temperatures of the two metalscomprising the respective contacts 13 and 23 and the deep vacuumenvironment in which they operate. Contacts of other materials could beused in a switch embodying the principles of this invention providedthat the material of the negative contact was one that did not producean effective cathode spot within the power levels for which the switchwas intended, and that the material of the positive contact did so; andprovided, of course, that such contacts were in a deep vacuum. However,tungsten and molybdenum are the preferred metals because both of themmelt at high enough temperatures to obviate the possibility of thecontacts being welded shut, and both are hard enough to resistmechanical wear that might in time produce frictional sticking.

While the tungsten/molybdenum contact pair of the switch of thisinvention undoubtedly has a higher resistance than contacts of thesofter metals, other factors pointed out hereinabove compensate for thisto provide the switch of this invention with a relatively low netresistance.

Of course the switch of this invention will not last forever. A certainamount of the molybdenum that is vaporized at each switch opening isdissipated to the wall of the envelope 7, and not all of the molybdenumthat is transferred to the tungsten contact 23 will be reengaged by thecontactor 12. Obviously the molybdenum that is deposited in locationswhere it is never again contacted by the molybdenum contact cannot takepart in cathode spot vaporization and therefore cannot be transferredback to the molybednum contact member. Hence after some hundreds ofmillions of operations in a high power DC circuit, the molybdenumcontactor will fail because of such dissipation of the material of itscontact portion. But with these considerations in mind, it is possibleto prolong the life of the switch by providing the contactor with acontact surface of substantial area, to afford the greatest possibleopportunity for transfer back to it of molybdenum deposited on thetungsten contact 23. To this end the wire ofthe bight portion of thecontactor is preferably flattened as shown in FIG. 6.

Besides affording long service life as explained above, molybdenum wiremakes a good contactor because it is duetile enough to be readily formedto the desired shape and has sufficient resiliency to provide thedesired biasing force. A further advantage of molybdenum wireis that itcontinues to support bending stresses at temperatures as high as l,400F. and above. This means that the contactor 12 can be bonded to the reed6 before that reed is heated to outgas it and fix its preload againstits post ll. Of course the contactor should be fastened to the reed 6with a preload substantially higher than that which it is intended tohave in the finished switch, since a certain amount of stress relievingof the contactor will occur as it is heated during outgassing of thereed assembly. However, if contactors are always assembled under aninitial preload which is equal to the yield point of the material, andthe reed assemblies are always heated to a particular maximum degassingtemperature such as l,500 F., the preload of the contactor against thereed 6 will always have a value, in the completed switch, that isdirectly related to the temperature to which it was heated.

From the foregoing description taken with the accompanying drawings itwill be apparent that this invention provides a magnetically operatedreed switch that is capable of closing and opening in very fast andfaithful response to the rapid buildup and decay of a magnetic actuatingfield; and that the switch of this invention is capable of controllingsubstantially high volt-ampere circuits in rapid cycling, with anextremely long service life even in DC applications.

What I claim as my invention is:

l. A switch having a pair of contact carriers arranged for relativemovement to and from engagement with one another under the influence ofa magnetic field and biased to normal relative positions in which theyare spaced a predetermined distance apart, said switch beingcharacterized by:

A. a first pair of contacts, both of high melting temperature material,one on each of said contact carriers, said contacts comprising theportions of the contact carriers that are engageable with one another;

B. acontactor 1. carried by one of said contact carriers for movementrelative thereto toward and from the other contact carrier,

2. said contactor having a biasing preload against said one contactcarrier in the direction toward said other contact carrier;

C. a third contact of high melting temperature material on thecontactor, normally spaced less than said predeter mined distance fromthe other contact carrier;

D. a fourth contact of high melting temperature material on said othercontact carrier, engageable by said third contact upon relative movementof the contact carriers towards engagement with one another; and

E. a hermetically sealed envelope, evacuated to a deep vacuum, enclosingsaid contact carriers, the contactor and said contacts.

2. The switch of claim 1, further characterized by:

A. the contacts of said first pair thereof being of tungsten;

B. said third contact being of molybdenum; and

C. said fourth contact being of tungsten.

3. A switch comprising a pair of contacts at least one of which ismovable toward and from engagement with the other, for repeatedlyopening and closing a circuit in which an electric current always flowsin the same direction at the time of separation of said contacts so thatat such times a first one of said contacts is always connected with thenegative terminal of the source of current for the circuit and the otherwith its positive terminal, said switch being characterized by:

A. means defining an evacuated hermetically sealed enclosure enclosingthe contacts by which they are maintained in a deep vacuum environment;

8. said first contact being of material having melting and vaporizingtemperatures at least about as high as those of tungsten; and

C. said other contact being of a material having lower melting andvaporizing temperatures than the material of the first. 4. The switch ofclaim 3, further characterized by: said other contact being ofmolybdenum. 5. A reed assembly for a reed switch, comprising anelongated, resiliently flexible reed having a free end and an anchoredend, and means defining a stop against which the free end portion of thereed is normally engaged under bias, said reed assembly beingcharacterized by:

the reed being a bimetal comprising a pair of elements which are bondedtogether along the length of the reed, 1. one ofsaid elements beingmagnetically permeable, 2. the rates of linear thermal expansion of saidelements being a. substantially similar at temperatures below a valuewhich is within the range of temperatures at which both elements willsustain stress, and

b. substantially different through a range of temperatures above saidvalue, and

3. the element having the higher rate of linear thermal expansion insaid range being at the side of the reed adjacent to said stop.

6. The reed assembly of claim 5, further characterized by:

A. said element at the side of the reed adjacent to the stop beingofNiromet 42"; and

B. the other element being ofKovar."

7. The reed assembly of claim wherein said stop comprises an elongatedpost, substantially stiffer than the reed, arranged in side-by-siderelation with the reed, further characterized by said reed having:

A. a substantially flat anchor portion adjacent to its anchored end thatflatwise overlies the post;

B. a substantially flat armature portion adjacent to its said other end;and

C. an integral neck portion between said anchor and armature portionsand connecting them, said neck portion having a cross section area lessthan that of the anchor and armature portions.

8. The reed assembly of claim 7, further characterized by:

A. the neck portion of the reed being of lesser thickness than theanchor and armature portions;

B. said neck portion being oblique to the anchor and armature portionsof the reed and being inclined away from the post and toward thearmature portion; and

C. the armature portion of the reed being oblique to the post with itsend portion adjacent to the neck portion spaced from the post and itsopposite end portion preloaded against the post.

9. The reed assembly of claim 8, further characterized by:

a contactor secured to the armature portion of the reed and having aspring arm overlying and preloaded against the surface of the armatureportion that is adjacent to the post, said spring arm extendinglengthwise beyond the tip of the armature portion and having a contactportion that projects away from the post across the tip of the armatureportion to normally extend beyond the plane of the surface of thearmature portion that is remote from the post.

10. The reed assembly of claim 5, further characterized by:

a contactor secured to the reed and having l. a spring arm portionoverlying said free end portion of the reed and preloaded against thesame in the direction away from the stop, said spring arm extendinglengthwise beyond the free end of the reed, and

2. a contact portion projecting laterally from the spring arm in thedirection away from the stop and across said other end portion of thereed a distance to normally extend beyond the plane of the surface ofthe reed that is remote from the stop.

11. The reed assembly of claim 10, wherein said contactor is ofmolybdenum wire, further characterized by:

a coating of tungsten on said other end portion of the reed at the sidethereof remote from the stop.

12. A switch of the type comprising an envelope enclosing a pair ofmagnetically permeable contact carriers, one of which comprises anelongated, resiliently flexible reed that is normally spaced apredetermined distance from the other contact carrier to define a gapbut is flexible into engagement with the other contact carrier under theinfluence of a magnetic field threading the contact carriers and thegap, said switch being characterized by:

A. the envelope being I. hermetically sealed and 2. evacuated to a deepvacuum;

B. a contactor carried by one of the contact carriers,

l. said contactor being preloaded against the contact carrier by whichit is carried, in the direction toward the other contact carrier, and

2. said contactor having a portion which normally projects partwayacross the gap toward said other contact carrier;

C. a molybdenum contact on said portion of the contactor;

and a D. a tungsten contact on said other contact carrier in a positionto be engaged by said molybdenum contact.

13. The switch of claim 12, further characterized by:

a tungsten coating on that portion of each contact carrier that engagesthe other, to provide an additional pair of cooperating contacts.

14. in a magnetically actuated switch:

A. an elongated, resiliently flexible, magnetically permeable reedhaving an anchored end and a free end; and

B. a contactor carried by the reed and comprising a single length ofresiliently flexible wire, the medial portion of which is bent to aU-shape, with legs and a bight portion, and each end portion of which isconnected with one of said legs around a loop and extends back along itsleg towards the bight portion,

. said end portion being flatwise secured to the reed near the free endthereof,

2. portions of the legs overlying one face of the reed and normallyengaging the same under flexing bias; and

3. the bight portion being bent out of the plane of said leg portionsand projecting across the free end of the reed beyond the plane of theother face thereof to provide a contact portion of the contactor.

15. The magnetically actuated switch of claim 14, further characterizedby:

A. said reed having 1. a substantially flat anchor portion adjacent itsanchored end,

2. a substantially flat armature portion adjacent its free end, and

3. an integral neck portion of smaller cross-sectional area connectingits anchor and armature portions and obliquely inclined to them;

B. the contactor having its said end portions overlying and secured toone face of the armature portion; and

C. said loops being edgewise spaced to opposite sides of the neckportion.

16. The magnetically actuated switch of claim 15, further characterizedby:

an elongated post, substantially stiffer than the reed, ex.- tendingalongside the reed adjacent to the first mentioned face thereof,substantially to the free end of the reed,

l. the anchor portion of the reed being flatwise engaged with andsecured to the post,

2. the neck portion of the reed extending obliquely away from the postand the anchor portion, and

3. the armature portion of the reed being preloaded toward the post.

17. The magnetically actuated switch of claim 16, further characterizedby:

said reed being a bimetal comprising l.Niromet 42" adjacent to the post,and

2. Kovar."

18. The magnetically actuated switch of claim 14, further characterizedby:

A. the contactor being of molybdenum wire; B. a tungsten contactengageable by the contactor upon flexing of the reed in the direction ofits said other face; and

C. a hermetically sealed envelope, evacuated to a deep vacuum, enclosingthe reed, the contactor and said tungsten contact.

19. The magnetically actuated switch of claim 16, further characterizedby:

the neck portion of the reed having a width not substantially less thanthat of the anchor and armature portions but having a lesser thicknessthan the anchor and armature portions.

20. A magnetically actuated switch of the type comprising a pair ofelongated, resiliently flexible, magnetically permeable reeds, eachhaving an anchored end and a free end, and means securing the anchoredends of the reeds at locations remote from one another and disposing thereeds with their free end portion in overlapping but laterally spacedapart relationship to define a gap between them, said switch beingcharacterized by:

A. a post for each reed, each of said posts being substantially stifferthan its reed and extending lengthwise along its reed at the sidethereof remote from the other reed;

B. the free end portion of each reed being normally engaged under biaswith its post;

C. a contactor secured to one of the reeds and having 1. a spring armportion overlying and preloaded against the surface of said reed that isadjacent to its post, said spring arm extending lengthwise beyond thefree end of said reed, and

2. a contact portion on said spring arm portion that projects across thefree end of said one reed partway across the gap to be engageable withthe other reed.

21. -An elongated reed for a magnetically actuated reed switch, saidreed having anchored and free ends and being characterized by:

A. a reduced thickness neck portion intermediate the ends of the reed,defining a substantially flat anchor portion adjacent its anchored endand a substantially flat armature portion adjacent its free end;

B. said neck portion of the reed being at a substantial oblique angle tothe anchor portion so as to be inclined lengthwise in one directionthereto; and

C. said armature portion being at an opposite oblique angle to the neckportion so as to be inclined lengthwise in the opposite direction to theneck and anchor portions.

22. The reed of claim 21, further characterized by:

an elongated post, substantially stiffer than the reed,

secured to the anchor portion and extending lengthwise along the reedsubstantially to its tip and substantially parallel to the anchorportion, said neck portion of the reed extending obliquely away fromsaid post and said armature portion of the reed being preloaded towardthe post.

23. The reed of claim 22, wherein said anchor, neck and armatureportions of the reed are integral with one another, furthercharacterized by:

said reed being a bimetal comprising 1. Niromet 42 adjacent to the post,and 2. "Kovar."

24. A magnetically actuated switch of the type comprising an elongated,resiliently flexible, magnetically permeable reed having an anchored endand a free end, a contact engageable by the free end of the reed, andmeans securing the anchored end of the reed at a location spaced fromthe contact and disposing the reed with its free end swingable towardand from engagement with the contact and normally spaced therefrom todefine a gap, said switch being characterized by:

A. a post for the reed, substantially stiffer than the reed andextending lengthwise along the reed at the side thereof remote from thecontact; B. the free end portion of the reed being normally engagedunder bias with the post; and

C. a contactor secured to the reed and having I. a spring arm portionoverlying and preloaded against the surface of the reed that is adjacentto the post, said spring arm portion extending lengthwise beyond thefree end of the reed, and

2. a contact portion on said spring arm portion that projects across thefree end of the reed partway across the gap to be engageable with thecontact.

25. A switching comprising a pair of contacts at least one of which ismovable toward and from engagement with the other, for repeatedlyopening and closing a circuit in which an electric current always flowsin the same direction at the time of separation, said switch beingcharacterized by:

A. means defining an evacuated hermetically sealed enclosure enclosingthe contacts by which they are maintained in a deep vacuum environment;

B. one of said contacts being of material having melting and vaporizingtemperatures at least about as high as those of tungsten;

C. electrically negative terminal means connected with said one contact;

D. the other of said contacts being of a material having lower meltingand vaporizing temperatures than the material of said one contact; and

E. electrically positive terminal means connected with said othercontact.

1. A switch having a pair of contact carriers arranged for relativemovement to and from engagement with one another under the influence ofa magnetic field and biased to normal relative positions in which theyare spaced a predetermined distance apart, said switch beingcharacterized by: A. a first pair of contacts, both of high meltingtemperature material, one on each of said contact carriers, saidcontacts comprising the portions of the contact carriers that areengageable with one another; B. a contactor
 1. carried by one of saidcontact carriers for movement relative thereto toward and from the othercontact carrier,
 2. said contactor having a biasing preload against saidone contact carrier in the direction toward said other contact carrier;C. a third contact of high melting temperature material on thecontactor, normally spaced less than said predetermined distance fromthe other contact carrier; D. a fourth contact of high meltingtemperature material on said other contact carrier, engageable by saidthird contact upon relative movement of the contact carriers towardsengagement with one another; and E. a hermetically sealed envelope,evacuated to a deep vacuum, enclosing said contact carriers, thecontactor and said Contacts.
 2. said contactor having a biasing preloadagainst said one contact carrier in the direction toward said othercontact carrier; C. a third contact of high melting temperature materialon the contactor, normally spaced less than said predetermined distancefrom the other contact carrier; D. a fourth contact of high meltingtemperature material on said other contact carrier, engageable by saidthird contact upon relative movement of the contact carriers towardsengagement with one another; and E. a hermetically sealed envelope,evacuated to a deep vacuum, enclosing said contact carriers, thecontactor and said Contacts.
 2. The switch of claim 1, furthercharacterized by: A. the contacts of said first pair thereof being oftungsten; B. said third contact being of molybdenum; and C. said fourthcontact being of tungsten.
 2. ''''Kovar.''''
 2. the neck portion of thereed extending obliquely away From the post and the anchor portion, and2. ''''Kovar.''''
 2. a contact portion on said spring arm portion thatprojects across the free end of the reed partway across the gap to beengageable with the contact.
 2. a substantially flat armature portionadjacent its free end, and
 2. portions of the legs overlying one face ofthe reed and normally engaging the same under flexing bias; and
 2. saidcontactor having a portion which normally projects partway across thegap toward said other contact carrier; C. a molybdenum contact on saidportion of the contactor; and D. a tungsten contact on said othercontact carrier in a position to be engaged by said molybdenum contact.2. evacuated to a deep vacuum; B. a contactor carried by one of thecontact carriers,
 2. a contact portion projecting laterally from thespring arm in the direction away from the stop and across said other endportion of the reed a distance to normally extend beyond the plane ofthe surface of the reed that is remote from the stop.
 2. the rates oflinear thermal expansion of said elements being a. substantially similarat temperatures below a value which is within the range of temperaturesat which both elements will sustain stress, and b. substantiallydifferent through a range of temperatures above said value, and
 2. acontact portion on said spring arm portion that projects across the freeend of said one reed partway across the gap to be engageable with theother reed.
 3. the element having the higher rate of linear thermalexpansion in said range being at the side of the reed adjacent to saidstop.
 3. an integral neck portion of smaller cross-sectional areaconnecting its anchor and armature portions and obliquely inclined tothem; B. the contactor having its said end portions overlying andsecured to one face of the armature portion; and C. said loops beingedgewise spaced to opposite sides of the neck portion.
 3. the bightportion being bent out of the plane of said leg portions and projectingacross the free end of the reed beyond the plane of the other facethereof to provide a contact portion of the contactor.
 3. the armatureportion of the reed being preloaded toward the post.
 3. A switchcomprising a pair of contacts at least one of which is movable towardand from engagement with the other, for repeatedly opening and closing acircuit in which an electric current always flows in the same directionat the time of separation of said contacts so that at such times a firstone of said contacts is always connected with the negative terminal ofthe source of current for the circuit and the other with its positiveterminal, said switch being characterized by: A. means defining anevacuated hermetically sealed enclosure enclosing the contacts by whichthey are maintained in a deep vacuum environment; B. said first contactbeing of material having melting and vaporizing temperatures at leastabout as high as those of tungsten; and C. said other contact being of amaterial having lower melting and vaporizing temperatures than thematerial of the first.
 4. The switch of claim 3, further characterizedby: said other contact being of molybdenum.
 5. A reed assembly for areed switch, comprising an elongated, resiliently flexible reed having afree end and an anchored end, and means defining a stop against whichthe free end portion of the reed is normally engaged under bias, saidreed assembly being characterized by: the reed being a bimetalcomprising a pair of elements which are bonded together along the lengthof the reed,
 6. The reed assembly of claim 5, further characterized by:A. said element at the side of the reed adjacent to the stop being of''''Niromet 42''''; and B. the other element being of ''''Kovar.'''' 7.The reed assembly of claim 5 wherein said stop comprises an elongatedpost, substantially stiffer than the reed, arranged in side-by-siderelation with the reed, further characterized by said reed having: A. asubstantially flat anchor portion adjacent to its anchored end thatflatwise overlies the post; B. a substantially flat armature portionadjacent to its said other end; and C. an integral neck portion betweensaid anchor and armature portions and connecting them, said neck portionhaving a cross section area less than that of the anchor and armatureportions.
 8. The reed assembly of claim 7, further characterized by: A.the neck portion of the reed being of lesser thickness than the anchorand armature portions; B. said neck portion being oblique to the anchorand armature portions of the reed and being inclined away from the postand toward the armature portion; and C. the armature portion of the reedbeing oblique to the post with its end portion adjacent to the neckportion spaced from the post and its opposite end portion preloadedagainst the post.
 9. The reed assembly of claim 8, further characterizedby: a contactor secured to the armature portion of the reed and having aspring arm overlying and preloaded against the surface of the armatureportion that is adjacent to the post, said spring arm extendinglengthwise beyond the tip of the armature portion and having a contactportion that projects away from the post across the tip of the armatureportion to normally extend beyond the plane of the surface of thearmature portion that is remote from the post.
 10. The reed assembly ofclaim 5, further characterized by: a contactor secured to the reed andhaving
 11. The reed assembly of claim 10, wherein said contactor is ofmolybdenum wire, further characterized by: a coating of tungsten on saidother end portion of the reed at the side thereof remote from the stop.12. A switch of the type comprising an envelope enclosing a pair ofmagnetically permeable contact carriers, one of which comprises anelongated, resiliently flexible reed that is normally spaced apredetermined distance from the other contact carrier to define a gapbut is flexible into engagement with the other contact carrier under theinfluence of a magnetic field threading the contact carriers and thegap, said switch being characterized by: A. the envelope being
 13. Theswitch of claim 12, further characterized by: a tungsten coating on thatportion of each contact carrier that engages the other, to provide anadditional pair of cooperating contacts.
 14. In a magnetically actuatedswitch: A. an elongated, resiliently flexible, magnetically permeablereed having an anchored end and a free end; and B. a contactor carriedby the reed and comprising a single length of resiliently flexible wire,the medial portion of which is bent to a U-shape, with legs and a bightportion, and each end portion of which is connected with one of saidlegs around a loop and extends back along its leg towards the bightportion,
 15. The magnetically actuated switch of claim 14, furthercharacterized by: A. said reed having
 16. The magnetically actuatedswitch of claim 15, further characterized by: an elongated post,substantially stiffer than the reed, extending alongside the reedadjacent to the first mentioned face thereof, substantially to the freeend of the reed,
 16. The magnetically actuated switch of claim 15,further characterized by: an elongated post, substantially stiffer thanthe reed, extending alongside the reed adjacent to the first mentionedface thereof, substantially to the free end of the reed,
 17. Themagnetically actuated switch of claim 16, further characterized by: 17.The magnetically actuated switch of claim 16, further characterized by:said reed being a bimetal comprising
 18. The magnetically actuatedswitch of claim 14, further characterized by: A. the contactor being ofmolybdenum wire; B. a tungsten contact engageable by the contactor uponflexing of the reed in the direction of its said other face; and C. ahermetically sealed envelope, evacuated to a deep vacuum, enclosing thereed, the contactor and said tungsten contact.
 19. The magneticallyactuated switch of claim 16, further characterized by: the neck portionof the reed having a width not substantially less than that of theanchor and armature portions but having a lesser thickness than theanchor and armature portions.
 19. The magnetically actuated switch ofclaim 16, further characterized by: the neck portion of the reed havinga width not substantially less than that of the anchor and armatureportions but having a lesser thickness than the anchor and armatureportions.
 20. A magnetically actuated switch of the type comprising apair of elongated, resiliently flexible, magnetically permeable reeds,each having an anchored end and a free end, and means securing theanchored ends of the reeds at locations remote from one another anddisposing the reeds with their free end portion in overlapping butlaterally spaced apart relationship to define a gap between them, saidswitch being characterized by: A. a post for each reed, each of saidposts being substantially stiffer than its reed and extending lengthwisealong its reed at the side thereof remote from the other reed; B. thefree end portion of each reed being normally engaged under bias with itspost; C. a contactor secured to one of the reeds and having
 21. Anelongated reed for a magnetically actuated reed switch, said reed havinganchored and free ends and being characterized by: A. a reducedthickness neck portion intermediate the ends of the reed, defining asubstantially flat anchor portion adjacent its anchored end and asubstantially flat armature portion adjacent its free end; B. said neckportion of the reed being at a substantial oblique angle to the anchorportion so as to be inclined lengthwise in one direction thereto; and C.said armature portion being at an opposite oblique angle to the neckportion so as to be inclined lengthwise in the opposite direction to theneck and anchor portions.
 22. The reed of claim 21, furthercharacterized by: an elongated post, substantially stiffer than thereed, secured to the anchor portion and extending lengthwise along thereed substantially to its tip and substantially parallel to the anchorportion, said neck portion of the reed extending obliquely away fromsaid post and said armature portion of the reed being preloaded towardthe post.
 22. The reed of claim 21, further characterized by: anelongated post, substantially stiffer than the reed, secured to theanchor portion and extending lengthwise along the reed substantially toits tip and substantially parallel to the anchor portion, said neckportion of the reed extending obliquely away from said post and saidarmature portion of the reed being preloaded toward the post.
 23. Thereed of claim 22, wherein said anchor, neck and armature portions of thereed are integral with one another, further characterized by: said reedbeing a bimetal comprising
 23. The reed of claim 22, wherein saidanchor, neck and armature portions of the reed are integral with oneanother, further characterized by: said reed being a bimetal comprising24. A magnetically actuated switch of the type comprising an elongated,resiliently flexible, magnetically permeable reed having an anchored endand a free end, a contact engageable by the free end of the reed, andmeans securing the anchored end of the reed at a location spaced fromthe contact and disposing the reed with its free end swingable towardand from engagement with the contact and normally spaced therefrom todefine a gap, said switch being characterized by: A. a post for thereed, substantIally stiffer than the reed and extending lengthwise alongthe reed at the side thereof remote from the contact; B. the free endportion of the reed being normally engaged under bias with the post; andC. a contactor secured to the reed and having
 25. A switching comprisinga pair of contacts at least one of which is movable toward and fromengagement with the other, for repeatedly opening and closing a circuitin which an electric current always flows in the same direction at thetime of separation, said switch being characterized by: A. meansdefining an evacuated hermetically sealed enclosure enclosing thecontacts by which they are maintained in a deep vacuum environment; B.one of said contacts being of material having melting and vaporizingtemperatures at least about as high as those of tungsten; C.electrically negative terminal means connected with said one contact; D.the other of said contacts being of a material having lower melting andvaporizing temperatures than the material of said one contact; and E.electrically positive terminal means connected with said other contact.